SAN DIEGO (AP), Two drug-smuggling tunnels with rail systems stretching hundreds of yards (meters) across the U.S.-Mexico border were discovered by law enforcement officials, and a 73-year-old woman was arrested on suspicion of helping run one operation, U.S. authorities said Friday.

No contraband was found in connection with the tunnels, which linked warehouses in Tijuana, Mexico, and the Otay Mesa area of San Diego, according to a statement from U.S. Immigration and Customs Enforcement's Homeland Security Investigations.

The first tunnel, stretching about 600 yards(550 meters), was discovered Tuesday. It was described as being equipped with lighting, a crude rail system and wooden trusses.

The entrance on the U.S. side is inside a warehouse where a cement cap covered a 70-foot(21-meter) shaft. A pulley system was installed to hoist goods into the building, which was filled with children's toys and boxes of televisions.

The other tunnel, located Thursday, stretches more than 700 yards(640 meters) and was built with more sophisticated features including a multi-tiered electric rail system and ventilation equipment.

On Wednesday, investigators with the San Diego Tunnel Task Force arrested the woman from the San Diego suburb of Chula Vista for investigation of overseeing the logistics at the location of the first tunnel. Her name was not immediately released.

The tunnels were the sixth and seventh found in the area in less than four years, ICE said.

U.S. Attorney Laura Duffy said the discoveries foiled cartel plans to sneak large quantities of drugs across the border.

``Going underground is not a good business plan,'' she said in a statement.

Other participants in the investigation include U.S. Customs and Border Protection and the Drug Enforcement Administration. Mexican law enforcement officials also assisted.